With conventional sources of uranium forecasted to be depleted within the century, research into the harvesting of uranium from seawater, which is estimated to contain 1000 times more uranium than land, is crucial to determining the continued viability of nuclear power generation. Recent studies have shown that the cost of harvesting uranium from seawater can be reduced by coupling the harvesting system with an existing off-shore structure, such as a wind turbine, to eliminate the need for additional moorings and increase the overall energy-gathering ability of the wind farm system. This paper presents the design, fabrication, and ocean testing of 1/10th physical scale prototypes of two such systems. Both designs utilize adsorbent filament that is enclosed in a hard permeable shell to decouple the mechanical and chemical requirements of the device.
The expanded use of nuclear power has the potential to significantly reduce carbon dioxide emissions from power generation, given that one gram of 235U can theoretically produce as much energy as burning 1.5 million grams of coal (Emsley 2001). However, at the current consumption rate, global conventional reserves of terrestrial uranium (approximately 7.6 million tonnes) could be depleted in a little over a century (OECD, 2014). As these reserves decrease, uranium is expected to come from lower quality sites leading to higher extraction costs and greater environmental impacts. Fortunately, the ocean contains approximately 4.5 billion tonnes of uranium, present as uranyl ions in concentrations of approximately 3 ppb (Oguma et al., 2011). A sustainable way to harvest uranium from seawater will provide a source of nuclear fuel for generations to come. It will also give all countries with ocean access a stable supply of uranium, thereby eliminating the need to store spent fuel for potential reprocessing, and helping to address nuclear proliferation issues.
Kim et al. 2013 found uranium adsorption by chelating polymers to be the most viable uranium recovery technology in terms of adsorption capacity, environmental footprint, and cost (Zhang et al., 2003, Seko et al., 2003, Anirudhan et al., 2011). In this technology, chelating polymers allow for the passive extraction of uranium from seawater by adsorption. They are deployed in the ocean and remain submerged until the amount of captured uranium approaches the adsorption capacity. From there, the metal ions, including uranium, are stripped from the polymer through an elution process. Current experimental data indicates that uranium is best eluted from the polymer in a highly alkaline bath if the polymer is to be reused. Following elution it is regenerated with an alkaline wash to remove any adhered organic matter. The output is transformed into yellowcake through a purification and precipitation process similar to that for mined uranium.
